1. Field of the Invention
The present invention relates to a valve unit employed in writing instruments or liquid applicators suitable for applying liquid such as ink, cosmetic liquid, paint, liquid drug, adhesive and the like.
2. Description of the Prior Art
Hitherto, in this field of the art, there is no valve unit for feeding the liquid always at a constant rate to a liquid-application member of the writing instrument or liquid applicator when the valve unit is opened.
Consequently, in a conventional type of the writing instrument or liquid applicator, it is difficult to feed the liquid to the liquid-application member of the applicator at a constant rate without fail, because a so-called push-out operation of the writing instrument or liquid applicator for opening the valve unit substantially always varies in the length of its manual operation time to cause an excess or a shortage of the application liquid in the liquid-application member. The excess of the application liquid in the liquid-application member drops from the liquid-application member to smudge articles such as paper being coated with the application liquid. On the other hand, the shortage of the application liquid in the liquid-application member produces thin spots in writing or painting operation of the applicator. This is a problem inherent in the conventional writing instrument or liquid applicator.